1. Field of the Invention
Embodiments of the present invention relate to a method, medium, and apparatus controlling a disk drive, and more particularly, to a method, medium, and apparatus compensating for torque variations depending on temperature in a seek servo operation to compensate for a difference between a model torque constant and an actual torque constant based on temperature variations in a disk drive.
2. Description of the Related Art
A data storage device, i.e., a hard disc drive contributes to a computer system operation by reproducing data from a disc or writing data to the disc using a magnetic head. With increasingly high capacity, high density, and compact structures of hard disc drives, a bit per inch (BPI) indicating a density in a rotating direction of a disc and a track per inch (TPI) indicating a density in a radial direction thereof have also been increasing. As a result, controlling mechanisms with finer control capabilities are desired.
A hard disc drive can include a plurality of magnetic transducers that read and/or write, respectively, information by sensing and magnetizing a magnetic field of a rotating disc. Information can be stored in a plurality of sectors positioned within an annular track, for example. Track numbers can be positioned across a surface of a disc, with numbers for vertically similar tracks being referred to as cylinder numbers, for example. Accordingly, here, each track may be defined by a cylinder number.
Each transducer can typically be integrated within a slider included in a head gimbal assembly (HGA). An HGA may be attached to an actuator arm, which has a voice coil positioned adjacent to a magnetic assembly. The voice coil and the magnetic assembly can define a VCM. A hard disc drive also typically includes a driving circuit and a controller to supply current that excites the VCM. The VCM can rotate the actuator arm and thereby move transducers across a surface of a disc.
When writing and/or reading information, the hard disc drive may perform a seek routine to move the transducers from one cylinder to another cylinder. During the seek routine, the VCM can be excited by current that moves the transducers to a new cylinder position across the surface of the disc. The controller can perform a servo routine to guarantee that the transducers are moved to an exact cylinder position and the center of a track.
Generally, it is preferable to minimize the time required to read information from or write information to a disc. Accordingly, the seek routine performed by the hard disc drive should be implemented so that the transducers are moved to a new cylinder position within a short period of time. In addition, the time required for stabilizing the HGA should be minimized so that the transducers can quickly write or read information and are positioned adjacent to the new cylinder at one time.
In seek mode, a seek current can be applied to the VCM by generating acceleration, velocity, and position trajectories for the transducers with respect to a seek distance and feeding back to the VCM errors between a design velocity and current velocity of the transducers and between a design position and current position of the transducers. Here, the design velocity and design position of the transducers can be determined based on the acceleration trajectory of the transducers with respect to the seek distance.
Head disk assemblies may have different torque constants when their VCMs or driving circuits have different performances. In addition, portions of a head disk assembly have different torque constants because the magnetic field generated by the magnet used in the VCM varies from portion to portion of the corresponding head disk assembly.
Thus, conventionally, a torque constant compensation table is formed by measuring a difference between a modeling torque constant of each portion of a head disk assembly for the VCM, which is determined during a stage of servo designing, e.g., during design or manufacture, and an actual torque constant of each portion of the head disk assembly for the VCM, e.g., during operation. The modeling torque constant for each portion of the head disk assembly can then be calibrated by referencing the torque constant compensation table.
However, the temperature of a hard disk drive may vary due to heat generated during operations or changes in the external environment. The variation of the temperature of the hard disk drive causes both the magnetic force of the magnet and the resistance of the voice coil to vary. The variation of the magnetic force of the magnet and the resistance of the voice coil also eventually causes a torque constant of each portion of the head disk assembly for the VCM to vary.
Thus, the variation of the temperature of the hard disk drive results in a difference between a modeling torque constant of each portion of the head disk assembly for the VCM and an actual torque constant of each portion of the head disk assembly for the VCM. A large difference between the modeling torque constants and the actual torque constants adversely affect the servo performance of the hard disk drive, so the hard disk drive cannot maintain its seek servo operation as precisely and quickly as it used to.